Research On Fast Method For Electromagnetic Radiation And Scattering Problems

The application of radar technology represents the most advanced development ofthe military industry. Predicting the radiation characteristics of antennas and thescattering performance of an arbitrarily shaped structure is essential in electromagneticsimulation for the radar system. Meanwhile, rapid development of the modern phasedarray radar technology poses extraordinary demands on multiband receivers and tunableshifter phase shifter. This thesis in mainly concerned with above research focuses. Asfollow we summarize the major contributions:1. A standard method of moments (MoM) formulated is used as the corealgorithm to deal with the efficient solution of electromagnetic problems. In view ofsome special situations, the basis function selection and the process of solving theintegral equations will be adjusted accordingly. For instance, the conductingcomponents is based on the surface integral equation (SIE) with RWG basis, thedielectric components is based on either the combined-field PMCHWT integralequations or volume integral equation (VIE) approach, the low frequency breakdownproblem can be solved via loop-tree basis functions etc. Numerical examples areperformed to demonstrate the validity of these schemes.2. This dissertation gives a comprehensive introduction to a series of wide-bandelectromagnetic characteristic analyses, including the theory of numericalapproximation, the inferential reasoning formula and the implementation steps.Impedance matrix interpolation technique, the asymptotic waveform evaluation (AWE)technique, the best uniform rational approximation and the adaptive Stoer-Bulirschfrequency-sampling method are demonstrated for analysis successively. Theeffectiveness of these approaches is the base of the following chapters.3. The use of wavelets is also in conjugation with the best uniform rationalapproximation to analyze the wide-band electromagnetic characteristic of thewire-surface objects. For the analysis of wire-surface objects, all the wire-surfacemodels are substituted by surface-surface models. It is shown that the use of wavelets asbasis functions produces a MoM matrix with substantial sparsity and then the radiationproblem can be solved more efficiently by Chebyshev approximation. To improve theaccuracy, the polynomial series is replaced by the Maehly series and the best uniformrational approximation is obtained.4. A highly efficient computational electromagnetic technique based upon thewell known PO formulation combined with modified IE-FFT and adaptiveStoer-Bulirsch frequency-sampling method is applied to wide-band analysis of antennas radiating in the presence of electrically large conducting platforms. Unlike previousIE-FFT method, by interpolating the Green’s function and introducing the concept ofthe empty groups, modified single-level FFT algorithm which is based on thesubdomain FFT acceleration is employed to reduce matrix storage and to accelerate allthe matrix-vector multiplications in both the linear system for the moments and theiterative solver. Otherwise, the correction of the near-interaction is avoided. For thefrequency response of electric currents, the SB algorithm using the rationalapproximation solution and the recursive rules is utilized to achieve fast frequencysweeping. Compared with the conventional hybrid low/high-frequency method, thenovel hybrid method utilizes fewer unknowns and requires less solution time due to theabove modifications.5. A novel two-dimensional Stoer-Bulirsch adaptive sampling method via thebivariate Chebyshev series that combines with integral equations (IE) for the fastanalysis of electromagnetic scattering involving dielectric objects in both the frequencyand angular domains simultaneously. The modified solution is expanded by thebivariate Chebyshev series and the Chebyshev nodes performed by rational function arechosen as the initial samples for the Stoer-Bulirsch algorithm employing an adaptivesampling. The innovative recursive rules are proceeding in both the frequency andangular domains simultaneously. Compared to the traditional two-dimensional fastsweep techniques based on the best uniform rational approximation, no moreinformation is needed except the initial value. Besides the original advantages thehybrid approach also makes the least number of sampling points required to satisfy theprecision criteria in the meantime. By the two-dimensional extensive application ofStoer-Bulirsch adaptive sampling method, the accurate and fast radar cross-sectionresults turn into precision adjusted, complexity simplified and reliable in high stability.6. A novel tunable dual-band phase shifter using defected ground structure (DGS)and stubs is presented. The conventional transmission line of phase shifter is substitutedwith stubs and DGS (rectangle ring) in proposed structure. Compared to a conventionaldigital phase shifter, the dual-band can be achieved by the proposed structure, at thesame time, the frequency of dual band can also be modified by tuning length and widthof stubs and rectangle ring of DGS. In additional, the insert loss, the return loss and thevariation of phase of the proposed structure are improved, to an extent. The measuredresults verified the results of design.